How should weep holes and vent holes of an orifice plate be oriented in a horizontal pipe?

A. Top of pipe
B. Three o’clock position
C. Bottom of pipe
D. Nine o’clock position
E. Side of the pipe

The idea behind weep holes and vent holes is to remove the fluid in the nonflowing state from the flow measurement system.

For gas service, the weep hole should be located at the bottom of the pipe (Answer D) to allow liquids that may be present upstream of the orifice plate to pass downstream.

For liquid service, the vent hole should be located at the top of the pipe (Answer A) to allow noncondensable gases that may be present upstream of the orifice plate to pass downstream.

Additional complicating factors

Orifice calculations should compensate for the flow that passes through the weep holes and vent holes during normal flowmeter operation.